Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $235.59   12.794%   $265.7314   $265.73   $265.75   $265.70  
  Purchase #2 $147.84   7.358%   $158.7181   $158.72   $158.70   $158.70  
  Purchase #3 $45.99   5.626%   $48.5774   $48.58   $48.60   $48.60  
  Purchase #4 $38.63   5.242%   $40.655   $40.66   $40.65   $40.70  
  Purchase #5 $237.62   8.498%   $257.8129   $257.81   $257.80   $257.80  
  Purchase #6 $207.35   4.751%   $217.2012   $217.20   $217.20   $217.20  
  Purchase #7 $57.32   12.475%   $64.4707   $64.47   $64.45   $64.50  
  7 purchase totals = $970.34       $1,053.1667   $1,053.17   $1,053.15   $1,053.20